The present invention relates to printing devices. More particularly, the present invention relates to an apparatus and method for drying printing composition on a print medium.
Printing devices, such as inkjet printers and laser printers, use printing composition (e.g., ink or toner) to print images (text, graphics, etc.) onto a print medium in a printzone of the printing device. Inkjet printers may use print cartridges, also known as xe2x80x9cpensxe2x80x9d, which shoot drops of printing composition, referred to generally herein as xe2x80x9cinkxe2x80x9d, onto a print medium such as paper, transparency or cloth. Each pen has a printhead that includes a plurality of nozzles. Each nozzle has an orifice through which the drops are ejected. To print an image, the printhead is propelled back and forth across the page by, for example, a carriage while ejecting drops of ink in a desired pattern as the printhead moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as thermal printhead technology. For thermal printheads, the ink may be a liquid, with dissolved colorants or pigments dispersed in a solvent.
In a current thermal system, a barrier layer containing ink channels and vaporization chambers is located between an orifice plate and a substrate layer. The substrate layer typically contains linear arrays of heating elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, the ink in the vaporization chamber turns into a gaseous state and forces or ejects an ink drop from a orifice associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the print medium, the ink is expelled in a pattern onto the print medium to form a desired image (e.g., picture, chart or text).
In order for the image to be fixed to the print medium so that it will not smear, the printing composition must be dried. The printing composition is dried by a combination of the solvent evaporating and the solvent absorbing into the print medium, both of which take time. Various factors control the amount of time required for a particular printing composition to dry. These factors include the type of print medium, the quantity of solvent in an printing composition, the amount of printing composition on the print medium, and ambient temperature and humidity. Ideally, the printing composition will be fixed to the print medium quickly to help prevent image smear caused by things such as premature handling, ink puddling and movement before drying which can cause printing defects such as ink coalescence and intercolor bleed, print medium cockle (print medium buckle toward a printhead), and print medium curl (curling along at least one edge of a print medium). Quickly fixing the printing composition to the print medium also helps maximize printing device throughput.
To reduce the amount of this time, the surface of some types of print media may be specially coated to help speed drying. Other means may also be used such as special chemicals, generally know as xe2x80x9cfixersxe2x80x9d, that are applied to print media before or after printing.
Each of these above-described techniques have certain disadvantages. For example, specially coated print media may be relatively more expensive than uncoated print media. Fixers may become depleted during printing, resulting in no fixer being applied for the remainder of a print job, possibly causing some or all of the aforementioned problems, or the stopping of a print job to supply additional fixer, resulting in decreased printing device throughput and possible color hue shift on any print medium for which printing was halted.
Various types of heating devices may also be used to heat print media before and/or after printing. Pressure may also be applied, alone or in combination with heat from a heating device, to help reduce this amount of time.
For example, at least some radiant heating devices have been used to apply infrared heat energy to the back side of print media in the print zone. Such radiant heaters may use a heat source that is hot enough to damage or ignite the print media. One way in which ignition was avoided involved limiting the amount of time the print media is exposed to the heat source. However, if there is a failure in the printing device which causes the print media to dwell too long (e.g., a print media jam or printing device power failure), then the print media is in danger of being burned. Another way in which ignition was avoided involved lowering the power delivered to the radiant heater, thereby reducing the amount of radiant heat energy delivered to the print media. However, at least one problem with this approach was that the amount of radiant heat energy delivered to the print media was reduced significantly which lowered the overall efficacy of the radiant heating device in fixing printing composition on print media.
As another example, conductive heating may be used in a printing device by using a vacuum to hold down print media against a heated surface. A potential disadvantage of such designs is that if the vacuum hold-down force is not quite strong enough to counter the tendency of the print media to cockle, then contact with the heater will be lost at those cockle locations. Once contact is lost, the heat transfer to the cockle-affected regions is reduced and the tendency to cockle will increase. Relatively higher levels of vacuum are needed to avoid this problem, thus adding to the cost of the printing device and making it more difficult to move the print media against this higher vacuum hold-down force.
Pressure generating devices, such as pressure rollers, can cause image smear. Also, pressure generating devices add to the overall cost, size and complexity of the printing device.
An apparatus and method that decreased the amount of time required to dry or fix printing composition to a print medium while avoiding the above-described problems associated with other techniques would be a welcome improvement. Accordingly, the present invention is directed to drying printing composition on a print medium quickly to help prevent image smear, ink coalescence, intercolor bleed, print media cockle, and print media curl. The present invention is also directed to helping maximize printing device throughput. The present invention is additionally directed to eliminating the need for specially coated media and fixers to accelerate drying.
Accordingly, an embodiment of an apparatus in accordance with the present invention for use in a printing device configured to dispose printing composition on a print medium includes a blower configured to provide an airflow. The apparatus also includes a heater configured to heat the airflow and a duct coupled to the blower and configured to conduct the heated airflow by the print medium to help dry the printing composition on the print medium. The apparatus further includes a vacuum box coupled to the heated airflow and configured to conduct the heated airflow under the print medium and further configured to provide a hold-down force on the print medium adjacent the vacuum box.
The above-described embodiment of an apparatus in accordance with the present invention may be modified and include at least the following characteristics, as described below. The heater may be positioned in the vacuum box. The apparatus may additionally include a vent coupled to the duct to exhaust a portion of the airflow from the duct during conduction through the duct.
The vacuum box may also include a grill coupled to the airflow and positioned to conduct the heated airflow under the print media and a restrictor configured to impede the airflow prior to conduction under the print medium so that a pressure under the print medium is less than an ambient pressure above the print medium, thereby providing a vacuum hold-down force on the print medium adjacent the grill. In such cases, the heater may be positioned beneath the grill.
An alternative embodiment of an apparatus in accordance with the present invention for use in a printing device configured to dispose printing composition on a print medium includes structure for providing an airflow. The apparatus also includes structure for convectively heating the print medium by conducting a heated airflow by the print medium to help dry the printing composition on the print medium. The apparatus further includes structure for providing a vacuum hold-down force on the print medium.
The above-described alternative embodiment of an apparatus in accordance with the present invention may be modified and include at least the following characteristics, as described below. The apparatus may additionally include structure for radiatively heating the print medium to help dry the printing composition on the print medium. The apparatus may also include structure for exhausting a portion of the airflow from the structure for convectively heating the print medium by conducting a heated airflow by the print medium to help dry the printing composition on the print medium.
Yet another alternative embodiment of an apparatus in accordance with the present invention for use in a printing device configured to dispose printing composition on a print medium includes a vacuum unit configured to generate an airflow and direct the airflow by the print medium to create a hold-down force on the print medium adjacent the vacuum unit. The apparatus also includes a plurality of heaters each of which is disposed in the airflow to convectively heat the airflow to help dry the printing composition on the print medium.
The above-described additional alternative embodiment of an apparatus in accordance with the present invention may be modified and include at least the following characteristics, as described below. At least one of the heaters may be disposed in the vacuum unit to radiate heat toward the print medium to further help dry the printing composition on the print medium. The vacuum unit may include a blower configured to provide an airflow and a duct coupled to the blower and configured to conduct the airflow by the print medium. The apparatus may also include a vent coupled to the duct to exhaust a portion of the airflow from the duct during conduction through the duct.
An embodiment of a method in accordance with the present invention for use in a printing device configured to dispose printing composition on a print medium includes generating an airflow. The method also includes heating the airflow and conducting the heated airflow by the print medium to help dry the printing composition on the print medium. The method further includes restricting the airflow to create a vacuum hold-down force on the print medium.
The above-described embodiment of a method in accordance with the present invention may be modified and include at least the following characteristics, as described below. The method may additionally include exhausting a portion of the airflow.
An alternative embodiment of a method in accordance with the present invention for use in a printing device configured to dispose printing composition on a print medium includes generating an airflow. The method additionally includes heating the airflow and convectively heating the print medium through movement of the heated airflow by the print medium to help dry the printing composition on the print medium. The method further includes restricting the airflow to create a vacuum hold-down force on the print medium.
The above-described alternative embodiment of a method in accordance with the present invention may be modified and include at least the following characteristics, as described below. The method may also include radiatively heating the print medium to further help dry the printing composition on the print medium.
The foregoing summary is not intended by the inventors to be an inclusive list of all the aspects, advantages, and features of the present invention, nor should any limitation on the scope of the invention be implied therefrom. This summary is provided in accordance with 37 C.F.R. Section 1.73 and M.P.E.P. Section 608.01(d). Additionally, it should be noted that the use of the word substantially in this document is used to account for things such as engineering and manufacturing tolerances, as well as variations not affecting performance of the present invention. Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.